Add a field to the compile unit of where we plan on splitting out

the debug info for -gsplit-dwarf so we can encode that location
in the skeleton cu.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175933 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/DebugInfo.h

@@ -203,6 +203,8 @@ namespace llvm {
     DIArray getSubprograms() const;
     DIArray getGlobalVariables() const;
 
+    StringRef getSplitDebugFilename() const { return getStringField(14); }
+
     /// Verify - Verify that a compile unit is well formed.
     bool Verify() const;
   };